Rebels are preparing assaults on major military targets following the government's rejection of their offer to participate in elections, according to official and guerrilla sources.

President Bush's new administration, meanwhile, is trying to persuade Salvadoran leaders to soften their negative response to the revolutionaries.The Marxist-led insurgents, who condemned and did all they could to frustrate five national elections since 1980, offered Tuesday to take part in this year's presidential balloting under certain conditions.

"We have made a proposal. To the degree that the other side does not respond positively, the masses see that the struggle must continue. The tendency toward violence is increasing," guerrilla commander Ana Guadalupe Martinez told reporters in Mexico City.

The proposal has caused intense debate in El Salvador and Washington, which has given more than $3 billion in aid to El Salvador. The country is the most favored recipient of U.S. funds in the Western Hemisphere this decade.

President Jose Napoleon Duarte said Wednesday of the guerrilla document: "This is not a proposal for peace. It is a proposal for war."

It was "plagued with unconstitutionalities," he said, foremost among them the guerrillas' demand that he postpone the elections from March 19 to September to allow for reforms and their participation. He also cited "threats to aggravate the conflict" if the proposal were rejected.

"We are preparing for a very strong military reaction," a high-ranking army officer told The Associated Press. He said military intelligence believes the rebels in the next two weeks will hit at least one important strategic target, probably in the capital.

The officer, who spoke on condition of anonymity, acknowledged the elections proposal enhanced an image of rebel willingness to pursue peace.

That also is the consensus among diplomats. Even government officials grudgingly admit it.

But Duarte's government considers the guerrilla document tactical and insincere. "A pretense to intensify violence," was how the official Sisal news agency described it.

Martinez, in interviews taped in Mexico and broadcast in El Salvador, indicated the rebels had little hope their proposal would be accepted by the incumbent Christian Democrats or the rightist Republican Nationalist Alliance.

The alliance, known as Arena, controls the legislature and leads presidential polls. The leftist Democratic Convergence is a distant third.

Arena leaders rejected the rebel proposal out of hand as "a trap" and "a siren's song."

The guerrillas said they would back the Convergence in an election. In the past, rebels denounced elections as a "U.S.-imposed counter-insurgency plan."

A source close to the guerrillas said the proposal is legitimate but that it also is designed "to underscore contradictions. It shows the Christian Democrats and Arena for what they are, that they are more interested in power than democracy and peace."

Major rebel attacks are imminent, he said.

State Department spokesman Charles Redman on Thursday sought to play down Duarte's rejection of key elements of the proposal. In comments to Washington reporters, he emphasized Duarte's positive assessment of the rebels' recognition of electoral legitimacy.

"Any proposal such as this is worthy of serious and substantive consideration," said Redman.

A Western diplomat in San Salvador said the Bush administration is trying soften Duarte's emphatic rejection.

"It's hard to convince the American Congress and people that there's a serious government and business class here when in less than 24 hours they come out with a flat-out `no' to a significant proposal," he said.